1. Technical Field
The present invention relates generally to semiconductor devices; and, more particularly, it relates to power amplification circuitry.
2. Related Art
Many traditional power amplifiers feed signal with a non-constant envelope into a power amplifier array. One type of power amplifier is an envelope elimination and restoration (EER) power amplifier wherein the non-constant envelope is fed into the power amplifier so that the control of how to bias the power amplifier array is governed primarily by the non-constant envelope. One method of biasing the elimination and restoration (EER) power amplifier is to adjust the bias voltage as a function of the envelope of the electrical signal. This real time adjustment to the bias voltage presents a number of difficulties. The characteristic input impedance of the power amplifier tends to fluctuate as a function of the bias voltage provided to it. Also, the characteristic output impedance of the power amplifier tends to fluctuate as a function of the bias voltage provided to the power amplifier. In addition, the ambient environmental conditions in which the power amplifier is placed tend to affect its characteristic impedance. Absent some sophisticated compensation algorithms, conventional technologies that employ analog voltage biasing suffer from deleterious operation in dynamic environments.
There are significant problems with conventional power amplifiers in terms of efficiency of the feeding of a signal with a non-constant envelope to the power amplifier array. One particular problem is that a bias point is chosen for optimal operation at one (peak) power level. However, the non-constant envelope is inherently non-constant, therefore the power amplifier is only energy efficient at the designated peak level. In order to make the power amplifier efficient over a range of output power, its bias must be continually modified, which is substantially difficult to do. This is due largely to the real-time modification and varying of the voltage that is given to the power amplifier array which is very inefficient in terms of energy consumption.
One attempted solution to overcome the problems associated with conventional power amplifiers was the introduction in the 1950s of the elimination and restoration (EER) power amplifier. The elimination and restoration (EER) power amplifier adapts the voltage level of the voltage bias for the power amplifier array to the envelope power level of the non-constant envelope that is required at the output. This solution is one that does provide for optimal voltage bias at a variety of non-constant envelope levels, but it has many deficiencies itself. That is to say, although the solution of the elimination and restoration (EER) power amplifier does present a solution to some problems associated with conventional power amplifiers, it nevertheless introduces some undesirable problems. First, the efficiency of the bias adaptation technique employed by the elimination and restoration (EER) power amplifier inherently requires an additional amplifier. Also, the calibration of the elimination and restoration (EER) power amplifier is of utmost importance to ensure that the waveform fidelity of the waveform that is being amplified maintains its original shape including its spectral content.
The envelope digital to analog converter (DAC) power amplifier is a subset of the elimination and restoration (EER) power amplifier. Here, a power amplifier array of a power amplifier is treated as a purely digital device wherein each power amplifier within the power amplifier array is turned ON/OFF as required by the specific application. Various sizes of power amplifiers are employed within a power amplifier array to realize the required output levels within various applications. The envelope digital to analog converter (DAC) power amplifier is a very efficient technique to obtain adjustable optimal output power levels using a power amplifier. However, the deficiencies of the envelope digital to analog converter (DAC) power amplifier are great, similar to the deficiencies of the elimination and restoration (EER) power amplifier. For example, waveform fidelity of an original signal can easily be compromised without very good calibration of the envelope digital to analog converter (DAC) power amplifier. In addition, the input impedance of the envelope digital to analog converter (DAC) power amplifier tends to change as a function of the voltage that is used to bias the envelope digital to analog converter (DAC) power amplifier. Similarly, the output impedance of the envelope digital to analog converter (DAC) power amplifier tends to change as a function of the voltage that is used to bias the envelope digital to analog converter (DAC) power amplifier.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.